The present invention relates to a method for determining the surface quality of a substrate. This substrate passes from an initial state into a converted state. The invention also relates to a substrate-converting machine for converting an initial substrate and obtaining a converted substrate. The substrate-converting machine is part of a packaging production line.
In the packaging industry, a production line delivers a converted product produced from an initial substrate introduced at the start. The substrate may be a virgin substrate. More often than not, the virgin initial substrate may undergo a conversion process, for example by being printed on in a printing process, or in embossing, creasing and/or cutting operations, in order to obtain blanks or boxes corresponding to the packaging when it is laid out flat.
The initial substrate in the form of a reel undergoing a conversion process may have already previously undergone one or more prior treatments and then been reconditioned, for example in the form of a new reel. In this case, an insetting operation is necessary for the following conversion process.
The converting machine comprises one or more elements. Each of these elements is capable of giving rise to various defects on the surface of the converted substrate, leading to quality concerns for the packaging produced.
Checking the print quality proves to be a necessary operation when the packaging manufacturer wishes to be able to ensure that a production batch will not be spoiled by defects. These defects are assessed according to various acceptability criteria, but the selection of packaging is mainly made according to a quality level criterion chosen as a function of the product that has to be packaged.
Checking the substrate after conversion, before or after cutting, with close observation of the converted substrate, of the blanks or of the boxes, is still currently carried out by eye. The operator searches for all the types of defect, for example those associated with printing, and adjusts the settings of the converting machine as a result, so as to eliminate or limit these defects, preferably as quickly as possible.
This checking is increasingly frequently carried out automatically on the production line. The blanks or boxes that do not comply with the minimum requirements of printing and/or cutting and/or creasing and/or embossing quality in relation to a sample considered to be free of defects are ejected before they are stacked in the receiving station. The device for automatically detecting defects is located following the final converting element, before the ejection station and before the cutting station.
In the case of what is known as a reel-to-reel application, that is to say one starting from a reel of initial substrate and leading to another reel, of converted substrate, a converted substrate which does not comply with the minimum requirements of printing and/or creasing and/or embossing quality in relation to a sample considered to be free of defects is identified and may be singled out.